Production of synthetic benzene



' hibitive.

Patented June 12, 1945 v 2,378,208 raonuo'rron or srn'rnnrrc BENZENEDonald L. Fuller and Bernard S. Greensfeider,

Oakland, Calif., assignors to Shell Development Company, San Francisco,Calif., a corporation of Delaware No Drawing. Application July 6,1942,

Serial No, 449,971

8' Claims. (01. 260-668 This invention relates to a process for theproduction of synthetic aromatic hydrocarbons and particularly syntheticbenzene.

In view of the limited supply of benzene available from coal tar,various processes have been proposed whereby this exceedingly importantchemical may be produced from other sources. The most important of theseother sources is petroleum and its related products.

One method for the production of benzene from petroleum involves theseparation and recovery of the naturally-occurring benzene found incertain low-boiling straight run and cracked gasoline fractions. Thissource is relatively unattractive. The available straight run naphthasusually contain only very small concentrations of benzene and the costof recovery is usually pro- Cracked naphthas contain large amounts ofolefins and some diolefins and, although the concentrations of benzeneare appreciable, the problem of recovery of the benzene is againdifficult and expensive.

Another method for the production of benzene from petroleum involves thesynthesis of benzene from n-hexane. This synthesis is effected bycontacting vapors of n-hexane under known cyclization conditions with acyclizing catalystmore particularly chromium oxide. This method has thedisadvantages that the process must be effected with short cycleoperations, the equipment costs are high, and the yields are relativelypoor. Consequently, although the process has been known for some timeand has been. the subiect of much experimentation, it has never beenpractically applied.

A third often-'proposed method for the pro duction of benzene frompetroleum involves the synthesis of benzene from the cyclohexane foundto occur in small percentages in certain naphtha fractions. This iseffected by first carefully fractionating the naphtha to separate afraction containing the highest concentration of cyclohexane, subjectingthe slaparated cyclohexane fraction to a catalytic dehydrogenationtreatment, and finally recovering or concentrating the benzene soformed. In this method any one of a large number of dehydrogenationcatalysts such as the oxides or sulfides of the heavy metals of roups IVto VIII of the periodic system of the elements can be used, the reactionmay be effected under substantial hydrogen pressure, and.

the recovery of the benzene from the dehydrogenated products presents nospecial difficulties. This method therefore is believed to be the mostpromising of the hitherto known methods.

It is now found that aromatic hydrocarbons and particularly benzene maybe produced directly by catalytic means from a totally differentstarting material, namely methyl cyclopentane. It is furthermore foundthat naphthenic petroleum fractions of suitable boiling range .containappreciable quantities of this hydrocarbon, and that such fractionsconstitute a suitable starting material-for the production of very largequantities of synthetic benzene of any desired degree of purity.

According tothe process of the present invention aromatic hydrocarbonsand particularly benzene are synthesized directly ,by catalytic meansfrom methyl cyclopentane. As a starting material pure methylcyclopentane or a methyl cyclopentane fraction consisting largely ofmethyl cyclopentane from any source may be employed. The most availableand inexpensive source of methyl cyclopentane is in the so-called.naphthenic distillates such as straight run distillates from naphthenlcpetroleums. Thus, for example, typical California petroleums containbetween about 0.3% and 0.6% methyl cyclopentane. Straight rundistillates, boiling, for example, between F. and 223 F., from suchpetroleums contain much higher concentrations,

for example, 5% to 12%. When the large amountsof these availabledistillates are considered, it is seen that-the potential supply ofbenzene producible by the process of the invention is indeed large. Thispotential supply of synthetic benzene, especially if added to thepotential supply producibleby the above-described known methods, greatlyenhances the available reserves.

According to the process of the invention such naphthenic' distillatesare subjected to a fractional distillation to separate a relativelynarrow boiling fraction containing substantially all of the methylcyclopentane present and as little of higher and lower boilingconstituents as the economy of the fractionation allows. By suitablefractionation a fraction boiling between 150 F. and 185 F. andcontaining about 30% to 40% methyl cyclopentane may be easily obtained.By fractionation to a narrower boiling range, for example 150 F. to F.,fractions consisting predominantly of methyl cyclopentane can beobtained. Such a fraction contains only about 1% to 12% of cyclohexane.

The methyl cyclopentane fraction is treated under appropriate conditionswith a specific catalyst, namely molybdenum oxide. Of the many commondehydrogenation catalysts such as chromium oxide, tungsten oxide,vanadium oxide,

titanium oxide, iron oxide, platinum, nickel, pai- V ladium, copper, andthe metal sulfide dehydrogenation catalysts, the only one found toafford the desired result is molybdenum oxide. Chromium oxide is totallyunsuitable. Certain ob- 1 active alumina, if this is employed, maysuitably be stabilized against conversion into inactive alpha alumina bythe admixture of a minimum amount of clay-or by the conversionof atleast the surface into an alumina of the spinel type, for instance byreaction with calcium oxide, magnesium oxide or the like. Effectiveamounts of molybdenum oxide to be applied to such carrier or supportingsubstances are, for instance, from about 4% to about 80% (i. e. 3% to22.5% molybdenum).

The treatment of the methyl cyclopentane with the above describedcatalyst may be effected under various conditions within the followingapproximate limits:

Temperature -C Pressure atm-- 2-25 Liquid hourly space velocity 0.1-1Partial pressure of hydrogen .-atm 1-30 By liquid hourly space velocityis meant the volumes of liquid contacted (in the vapor form) per volumeof catalyst per hour. Thus, a liquid hourly space velocity of 3signifies that for every volume of reactor space filled with catalystthere is fed the vapors of three volumes of liquid.

Suitable preferred conditions are for example:

Temperature ..C About 490 Pressure About Liquid hourly space velocityAbout 0.5

Partial pressure of hydrogen..---atm About '7 Since these conditions aresubstantially equivalent to the conditions commonly employed inhydroforming higher boiling gasolines, they will be referred tohereinafter and in the appended claims as hydroforming conditions."

When treating the above-described methyl cyclopentane fractions underthese conditions the following reaction predominates:

Side reactions, such as cracking and condensation to polynuclearhydrocarbons, etc., take place only to a minor extent. The conversionproduct therefore consists essentially of benzene with lesser amounts ofpolynuclear aromatic hydrocarbons.

The treatment of the methylcyclopentane or methylcyclopentane fractionmay be effected in ,any one of the known suitable manners for effectingsimilar reactions, such as hydroforming,

with similar catalysts. Thus, the catalyst may be employed in a finelydivided, granular, or pelleted form in converters of suitable design forsuch catalysts. A suitable method is, for example, to support thecatalyst in granular or pelleted form in a reaction converter providedasvaaos with heating and temperature controlling means and to pass thevaporized methyl cyclopentane fraction in admixture with, for example,from 2 to 5 volumes of hydrogen therethrough. The catalyst isperiodically regenerated by burning oif deposited carbonaceous matterwith oxygen or an oxygen-containing gas in the known manner.

The product obtained from the catalytic treatment contains large amountsof benzene, for example, 40-70%. This product may be used per so, ifdesired, but it is most advantageously treated to recover the benzene ina pure or more concentrated form. For example, the product may be simplyfractionally distilled to recover a relatively pure benzol or a crudebenzol which may be further refined in the manner now used for therefining of coal tar benzol. Also, the benzene may be recovered eitherwith or without a preliminary fractionation, by solvent extractionand/or azeotropic or extractive distillation in the known manner. Thebenzene produced by the present process is relatively free of sulfurcompounds and in this respect is superior to the coal-tar product.However, a wash with dilute sulfuric acid is sometimes required as afinal finishing step. In this way substantially pure benzene which canbe made to meet the most rigid specifications may be efiicientlyproduced.- The process of the invention is illustrated by the followingexamples which it is to be understood are not intended to limit theinvention in any way.

Example I Methyl cyclopentane was vaporized, the vapors mixed with 5volumes of hydrogen and the mixture passed over a molybdenumoxide-alumina catalyst (14% M0) at a temperature of 490 C., a pressureof 20 atmospheres and a contact time of about 100 seconds. The yield ofliquid product was 79% by volume (the theoretical volume yield based on100.; conversion of the methyl cyclopentane to benzene is 79%) and theproduct contained about 2% by weight olefins. The

weight percentages of aromatics in theproduct after various periods oftreatment without regeneration of the catalyst were as follows:

Methyl cyclopentane was converted as described in Example I except thatthe mole ratio of hydrogen to methyl cyclopentane was '3 and the totalpressure was 10 atmospheres. The

7 weight percentages of aromatics in the product after various periodsof treatment without re-- generation of the catalyst were as follows Percent aromat- Hours its In later experiments with the same catalyst underthe same conditions the corresponding yield of aromatics was:

Per cent Per cent Hours aromat- Hours aromatics ics Example II I Iercent aromatics Eonrs 50 sec. 30 sec.

-We claim as our invention:

1. A process for the production of benzene which comprises treating ahydrocarbon fraction consisting essentially of methyl cyclopentan underhydroforming conditions with a molybdenum oxide catalyst and producebenzene as principal conversion product.

2. A process for the production of benzene which comprises treating ahydrocarbon. fraction consisting essentially Of methyl cyclopentaneunder hydroforming conditions with a molybdenum oxide-alumina catalystand produce benzene as principal conversion product.

3. A process for the production of benzene which comprises treating ahydrocarbon fraction consisting essentially of methyl cyclopentane under hydroforming conditions with a catalyst consisting essentially of anactive alumina impregnated with molybdenum oxide and produce benzene asprincipal conversion product.

4. A process for the production of benzene from naphthenic petroleumdistillates which comprises fractionally distilling a naphthenicpetroleum distillate to separate a. methyl cyclopentane fraction boilingpredominantly between 150 F. and 185 F. and treating said methylcyclopentane fraction under hydroforming conditions with a molybdenumoxide catalyst so a to produce benzene as predominant conversionproduct.

5. A process for the production of benzene from naphthenic petroleumdistillates which comprises fractionally distilling a naphthenicpetroleum.

distillate to separate a methyl cyclopentane fraction boilingpredominantly between 150 F. and 185 F. and treating said methylcyciopentane fraction under hydroforming conditions with a molybdenumoxide-alumina catalyst so as to produce benzene as predominantconversion product.

6. A process for the production of benzene from naphthenic petroleumdistillates which comprises fractionally distilling a naphthenicpetroleum distillate to separate a methyl cyclop'entane fraction boilingpredominantly between 150 F. and 185 F. and treating said methylcyclopentane fraction under hydroforming conditions with a.

catalyst consisting essentially of an active alumina impregnated withmolybdenum oxide so as to produce benzene a predominant conversionproduct. 1

7. A process for the production of benzene which comprises passing a.hydrocarbon fraction consisting essentially of methylcyclopentane over acatalyst comprising molybdenum oxide under hydroforming conditions sothat benzene is produced as predominant conversion product.

8. A process for the production of benzene which comprises contacting ahydrocarbon fraction consisting essentially of methylcyclopentane withmolybdenum oxide at 450 to 525 C. under a partial pressure of hydrogenof 1 to 30 atmospheres and at a liquid hourly space velocity for thefraction treated of 0.1 to 1.

DONALD L. FULLER. BERNARD S. GREENSFELDER.

